1. Field of the Invention
Embodiments of the invention relate to a shielding device for shielding an electronic component from magnetic and electric fields to be mounted on a printed circuit board, to a printed circuit board and to an electrically driven implant comprising a shielding device according to the invention. Furthermore, embodiments of the invention relate to a method of shielding an electronic component to be mounted on a printed circuit board. In particular, embodiments relate to an electrically driven implant, such as a defibrillator, comprising a shielding device for shielding a transformer.
2. Description of the Related Art
Shielding devices, such as shielding hoods, shielding caps or shielding cans for shielding electronic components, are principally known in the art. Such shielding devices primarily serve for reducing electromagnetic interference (EMI) between external electromagnetic radiation and electromagnetic radiation originating from the electronic component to be shielded. In particular, a shielding device can serve for preventing an external static magnetic field to enter the room sheathed by the shielding device.
The electronic component to be shielded can be an active electronic component, such as an integrated circuit, a power switch, a transistor or a passive electronic device, such as a resistor, a capacitor, an inductor or a transformer.
For reducing EMI, the known shielding devices are usually imposed over the electronic component, which is in most cases mounted to a printed circuit board. The known shielding devices are either fixed to the electronic component to be protected or to the printed circuit board. The latter case is, for instance, described in the U.S. Pat. No. 7,488,901.
FIG. 1 shows several views of an unshielded transformer as an example of a prior art electronic component. Such a transformer is, for instance, incorporated in an implantable defibrillator. If the transformer is operated in the presence of a strong external magnetic field, as can happen when an external programming device containing a strong permanent magnet is brought in close proximity to the defibrillator, a core of the transformer can saturate due to the strong external magnetic field. Such saturation can significantly reduce the operating efficiency of the transformer and, furthermore, can lead to a transformer failure.
A complete shielding of the transformer depicted in FIG. 1 is not possible with means of known shielding devices due to a plurality of attachment pins 1 which serve for attaching the transformer to a printed circuit board.
For shielding the transformer of FIG. 1, a shielding cap according to FIG. 2A is known. The known shielding cap comprises a top part 12 and a bottom part 14. Due to the attachment pins 1, the bottom part 14 of the known shielding cap exhibits cutouts 16 arranged at a side or, respectively, a corner. Because of these cutouts, the transformer 1 cannot be sheathed completely by the known shielding cap, resulting in an insufficient EMI protection. The gaps of the known shielding cap due to the cutouts 16 are also marked in FIG. 2C.
In addition to an insufficient EMI protection, the known shielding cap of FIG. 2A furthermore constrains the mechanical robustness of the electronic component be shielded, as it additionally has to be fixed to the electronic component. As depicted in FIG. 2B, an electronic component can often be constructed of multiple single parts, such as, in case of a transformer, a magnetic core 2, a bobbin 3, an insulation wrapper 4, which are all mounted together on top of attachment pins 1. Not shown are the wires, which wind around the bobbin 3 and terminate onto the top of the attachment pins 1.
Due to limited space, the amount of attachment pins is also limited and a robust mechanical support for heavy components, as the transformer, cannot be ensured.